Cam phasers are well known in the automotive art as elements of systems for reducing combustion formation of nitrogen oxides (NOX), reducing emission of unburned hydrocarbons, improving fuel economy, and improving engine torque at various speeds. As is known, under some operating conditions it is desirable to delay or advance the closing and opening of either the intake valves or the exhaust valves or both, relative to the valving in a similar engine having a fixed relationship between the crankshaft and the camshaft.
Typically, cam phasers employ a first element driven in fixed relationship to the crankshaft and a second element adjacent to the first element and mounted to the end of the camshaft in either the engine head or block. In modem automotive engines, the camshafts are typically disposed in the engine head for direct actuation of the valve tappets. Cam phasers are commonly disposed at the crankshaft and camshaft ends opposite the engine flywheel, herein referred to as the "front" end of the engine.
The first and second phaser elements are connected typically in one of two ways to cause the crankshaft to rotate the camshaft. In the older known art, a helically-splined coupling between the elements is driven axially by a hydraulic ram such that axial motion of the ram is translated into change of rotational phase between the two elements.
In the newer known art, the first element is typically a cylindrical stator mounted coaxially to a crankshaft-driven gear or pulley and having a plurality of radially-disposed chambers and an axial bore, and the second element is a vaned rotor mounted to the end of the camshaft through the stator bore and having a vane disposed in each of the stator chambers such that limited relative rotational motion is possible between the stator and the rotor. The chambers are sealed typically by front and rear face seals of the stator. The apparatus is provided with suitable porting so that hydraulic fluid, for example, engine oil under engine oil pump pressure, can be brought to bear controllably on opposite sides of the vanes in the chambers. Control circuitry and valving, commonly a multiport spool valve, permits the programmable control of the volume of oil on opposite sides of each vane to cause a change in rotational phase between the stator and the rotor, in either the rotationally forward or backwards direction.
A serious problem is known in adapting existing engine designs to cam phasers. A cam phaser can occupy considerable volume in the region immediately beyond the end of the camshaft and can also substantially complicate positioning of the first cam bearing and routing of oil passages in the engine head. Existing engine designs and manufacturing tooling typically provide little unoccupied space for such addition within the engine envelope, especially within the cam cover. Extending the length of the cam cover and head specifically to accommodate a phaser generally is prohibitively expensive and not feasible; thus, phasers typically are incorporated into engines only when an entirely new engine design is put forth, for example, the Unitech phaser in the BMW M50 engine, the Mercedes phaser in the 500SL 5-litre engine, and the INA phaser in the Ford Escort Zetec engine.
Further, known hydraulically-driven phasers typically utilize pressurized engine oil which can contain significant amounts of sludge and/or engine-manufacturing debris which can foul or damage moving parts of a phaser, especially the spool valve typically used to regulate flow to the chambers. Some phasers, for example, the INA phaser noted above, have the spool valve within the cam cover where it is not readily accessible for service or repair.
Further, known phasers are not fully modular and can require careful, tedious assembly of components in sequence onto the camshaft. In addition, some known phasers require substantial modification to the end of the camshaft, for example, hydraulic porting.
What is needed is a front-mounting cam phaser module a) containing stator, rotor, control valve and electrical connectors, and inline oil filter which can be assembled and tested off-line; b) requiring minimal redesign and no lengthening of the cam cover and head; c) requiring no or minimal modification of the camshaft; d) providing simple attachment as a module to the camshaft and head of an existing-design engine; and e) resulting in minimal increase in the overall length of the engine.